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Cylindritic Structures Of Isotactic Polypropylene Molded By Sequential Co-injection Molding

G. Wang, Y. Zhou, Songjie Wang, J. Chen, X. Zhang, Sheng Lu
Published 2013 · Materials Science

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In this study, isotacitc polypropylene (iPP) samples were prepared by conventional injection molding (CIM) and sequential co-injection molding (SCIM), in which two kinds of polymer melt were injected into the mold cavity one after the other. The morphological structure of the samples was investigated by polarized light microscopy (PLM) and scanning electron microscopy (SEM). Results show that the structures of the samples prepared by CIM have a typical skin-core structure. This structure could be divided into three layers along the thickness direction of the samples: skin layer, transition region and core layer. However, the morphologies of the samples prepared by SCIM have a fascinating supermolecular structure that can not be roughly divided into three layers. A region of cylindritic structures, which is rare in CIM, is formed between the skin layer and the core layer of the second injected material. In particular, the cylindritic structures are more easily found when the melt temperature is relatively lower and the delay time is longer. The results were further interpreted based on the analysis and comparison of the thermo-mechanical history imposed on the melt during the CIM and SCIM processes.
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